It has been possible to form laminated glass articles, such as laminated tubing and laminated sheet glass, wherein a continuous flow or stream of the composite glass is delivered to form such tubing or sheet as desired. U.S. Pat. No. 4,023,953 illustrates a method and apparatus for continuously producing composite glass tubing.
U.S. Pat. No. 3,582,306 describes method and apparatus for continuously forming a composite sheet or ribbon of molten glass directly from a plurality of flows of molten vitreous material and U.S. Pat. No. 3,582,454 discloses method and apparatus for forming articles, such as plates and cups, from such continuous sheet of the composite material. In this patent molten glass is described as being delivered to first form a continuous composite sheet which is subsequently formed and trimmed into articles.
The thus described prior art related to the formation of composite articles, such as tubing and sheet from a continuous flow of a composite glass. The selection of the glass compositions, such as those disclosed in U.S. Pat. No. 3,673,049, may be such as to provide a strengthened blown or pressed laminated article having a compressive outer skin according to a recently issued U.S. Pat. No. 4,457,771, which discloses the concept of forming laminated articles having a core of one glass completely surrounded by a skin of a second glass. A descrete charge of molten glass is formed from a plurality of separate and distinct glasses in such a manner that each charge has a core glass of one composition completely encapsulated within and surrounded by a skin glass of a second composition. The descrete charge is delivered while in a molten state to a mold or forming surface wherein a positive force is applied thereto, such as pressing or blowing to form a laminated article. The delivery apparatus for forming the laminated charge in U.S. Pat. No. 4,457,771 is described as comprising a core glass container having an orifice opening and an outer skin glass container having an orifice opening concentric with but below the core glass central orifice opening. The core glass container is provided with suitable conduit means for delivering molten core glass from a suitable supply thereof, such as a melting tank. In a like manner, the outer skin glass container is provided with suitable conduit means for supplying molten skin glass from a supply thereof, such as a melting tank, to the outer container. A pneumatic bell immersed in the core glass container is used to apply pressure or vacuum as desired. Likewise, a baffle extending into the skin glass container is described as being connected to a source of pressure or vacuum for controlling the flow of skin glass.
While the described prior art suggests making an encapsulated, composite gob of two separate glass compositions and teaches a method and apparatus for forming the charge or gob, there is no teaching or suggestion of using soda-lime-silica glasses of generally similar characteristics with the skin glass being essentially the same as the core glass with the core glass viscosity-versus-temperature curve being very similar to the viscosity-versus-temperature curve of the skin glass and at the log 3 viscosity having essentially identical temperature. Thus the glasses are capable of being fed to a gob feeder at essentially the same temperatureviscosity condition to permit formation of "cased" gobs or charges of molten glass.